San Francisco 49ers starting quarterback Nick Mullens (4) hands the ball off to San Francisco 49ers' Matt Breida (22) against the Seattle Seahawks in the second quarter at Levi's Stadium in Santa Clara, Calif., on Sunday, Dec. 16, 2018. (Nhat V. Meyer/Bay Area News Group)

San Francisco 49ers starting quarterback Nick Mullens (4) sits on the bench during their game against the Seattle Seahawks in the fourth quarter at Levi's Stadium in Santa Clara, Calif., on Sunday, Dec. 16, 2018. (Nhat V. Meyer/Bay Area News Group)

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SANTA CLARA — An interception-free, 275-yard game from Nick Mullens made life a lot easier for the 49ers in Sunday’s 26-23, overtime win against the Seattle Seahawks.

It also makes it harder for them next summer when they debate what to do with Mullens.

The starting quarterback job is reserved for Jimmy Garoppolo and his reconstructed left knee.

No one will condemn the 49ers if they keep Mullens and C.J. Beathard on the roster until Garoppolo’s health is proven, perhaps up to the midseason trade deadline.

SANTA CLARA, CA – DECEMBER 16: San Francisco 49ers starting quarterback Nick Mullens (4) sits on the bench during their game against the Seattle Seahawks in the fourth quarter at Levi’s Stadium in Santa Clara, Calif., on Sunday, Dec. 16, 2018. (Nhat V. Meyer/Bay Area News Group)

Mullens, an undrafted rookie last year, has greater trade value than Beathard, a 2017 third-round pick. Mullens’ stock is climbing with each win. Sunday’s was his third in four home games, the lone loss coming when the defense coughed up a fourth-quarter lead to the New York Giants.

“He’s playing like a top-half quarterback in this league,” cornerback Richard Sherman said. “You’ve got guys out there not playing better than Nick Mullens. He can be a starter for a lot of teams and we appreciate having him. He’s playing his tail off for us.”

Which teams? Let’s survey the league for some potential suitors.

–The Jaguars are done with Blake Bortles.

— Washington’s future with Alex Smith is uncertain, but he’s thankfully out of the hospital after infection from leg surgery.

— John Elway is perpetually looking for the next John Elway in Denver.

“You know, today I was focused on the game one play at a time and really just trying to end the streak against the Seahawks. It’s pretty cool that we got to do that as a team today.”

That team-oriented approach is endearing. Mullens has self-confidence, but not overly so.

He has that innate ability to make a play, not so much as a strong-armed gunslinger but as a determined leader who’ll stick in the pocket and trust his cast of linemen, receivers and running backs.

Those are the qualities Shanahan covets in a quarterback. Make no mistake, Garoppolo is his QB1 next year. Garoppolo is currently progressing well in his knee rehabilitation, and he was seen in Sunday’s postgame locker room cordially talking with 49ers co-owner John York.

Each week, Mullens is perhaps convincing the 49ers he should not go elsewhere next year, and he certainly won’t be going back to the practice squad, nor is he eligible now that he’s played six games.

Shanahan has kept his praise in check, complimenting Mullens on Sunday for being “very efficient” and improvising when needed. Last week, Shanahan said Mullens was “dead even” for an impending 2019 competition with Beathard, who went 1-4 last year and 0-5 this season in the QB2 role.

Shanahan would have preferred Mullens led a winning drive Sunday at the end of the fourth quarter, not overtime. Breakdowns on the line were a contributing factor.

Said Shanahan: “They got us on a few protection issues though. Nick ended up holding onto the ball, at least not turning it over.

“So I was happy with Nick. Gave us a chance to win.”

If not him, which quarterbacks might be on the market this coming offseason?

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All the Chiefs had to do to give QB Patrick Mahomes a chance in overtime was not allow a touchdown. They couldn't do it. That's the fault of their defense. The NFL overtime system is fine the way it is.